AX88772 controllers. ASIX added a new feature for AX88178/AX88772
controllers which allows combining multiple TX frames into a single
big frame. This was to overcome one of USB limitation where it
can't generate more than 8k interrupts/sec which in turn means USB
ethernet controllers can not send more than 8k packets per second.
Using ASIX's feature greatly enhanced TX performance(more than 3~4
times) compared to 7.x driver. However it seems r184610 removed
boundary checking for buffered frames which in turn caused
instability issues under certain conditions. In addition, using
ASIX's feature triggered another issue which made USB controller
hang under certain conditions. Restarting ethernet controller
didn't help under this hang condition and unplugging and replugging
the controller was the only solution. I believe there is a silicon
bug in TX frame combining feature on AX88178/AX88772 controllers.
To address these issues, reintroduce the boundary checking for both
AX88178 and AX88772 after copying a frame to USB buffer and do not
use ASIX's multiple frame combining feature. Instead, use USB
controller's multi-frame transmit capability to enhance TX
performance as suggested by Hans[1].
This should fix a long standing axe(4) instability issues reported
on AX88772 and AX88178 controllers. While I'm here remove
unnecessary TX frame length check since upper stack always
guarantee the size of a frame to be less than MCLBYTES.
Special thanks to Derrick Brashear who tried numerous patches
during last 4 months and waited real fix with patience. Without
this enthusiastic support, patience and H/W donation I couldn't fix
it since I was not able to trigger the issue on my box.
Suggested by: hselasky [1]
Tested by: Derrick Brashear (shadow <> gmail dot com>
H/W donated by: Derrick Brashear (shadow <> gmail dot com>
PR: usb/140883
65c12bf571